The present invention relates to a pattern recognition apparatus for recognizing impressed characters, printed characters or the like.
It is generally desirable that the pattern recognition apparatus of the type described have a high rate of proper character recognition and be operable at a high character reading speed. One prior pattern recognition process, known as a matrix matching method, will be explained with reference to FIG. 1 of the accompanying drawings. According to this method, features called a weight pattern are predetermined for each character, there being shown a weight pattern for the letter "B". More specifically, a region containing the letter is divided into a plurality of subregions which are weighted (as shown by numerals). Different characters are weighted differently. Therefore, any desired character can be recognized by comparing the weight pattern (input pattern) of the character as read with the weight pattern of a reference character.
This known method however is disadvantageous in that the degree of registration between characters is rendered variable and unstable because of relative positional displacement of the weight pattern of a reference character and that of a character as read, and variations in the widths of character strokes. To eliminate the foregoing disadvantage, the applicant has proposed a character recognition method using a shape matrix (see applicant's Japanese Patent Application No. 56-17570). According to this recognition process, each character is broken up into 72 subregions of 9.times.8, a shape matrix is set up for each character by determining whether there is a pattern in the subregions or not, and a character is recognized by comparing the shape matrix with a standard matrix. However, where an impressed character is to be read, the shape matrix of the character tends to vary due to a depression on the surface on which the character is impressed, and due to the presence of dirt such as soot on the surface, and therefore it is difficult to obtain correct character recognition. Another drawback is that only a limited number of characters, i.e. not more than 10, can be recognized using a 9.times.8 sized matrix.